Update: High energy photon pairs Search for RS-1 Gravitons Vladimir Litvin, Toyoko Orimoto Caltech QCD Meeting 11 December 2007
Introduction Feasiblity study for RS-1 G* Relevance to QCD group: QCD backgrounds are amongst our largest MC Samples: Produced privately at Caltech & Fermilab (no pileup) CMSSW_1_6_7 Signal RS-1 G: MG=750, 1250, 1000, & 1500 GeV (with c = 0.1 & 0.01) Main Backgrounds: Irreducible qqbar & gg (Born & Box) Gamma+jets (Brem), in which one photon comes from the hard interaction, and the second comes from FSR from an outgoing quark OR the decay of a neutral hadron QCD jets: where we get photons from the decay of neutral hadrons
MC Samples Signal Samples Background Samples Box and Born produced with CKIN(3)=200 (low limit of the invariant mass of the two outgoing photons, with high end is set to infinity). Filters were used when producing Brem and QCD samples, with selection rates 1:80 and 1:1200, respectively.
HLT EG Efficiency e- related HLT paths HLT1EMHighEt: 1 SC with pt>80 GeV and loose isolation: ECAL isol: < 5 GeV in R<0.3 + H/E: <5% , HCAL isol + <8 GeV in 0.15<R<0.3 + tracker iso: <4 tracks in R<0.3 HLT1EMVeryHighEt: 1 Super-Cluster (SC) with pt>200 GeV
Selection: Invariant Mass Signal Samples 750 =15 1000 =19 1250 =22 1500 =28 Background Samples Born Box Brem QCD Only requirement here: photon SC pt > 100 GeV… “final” cut is a 3window around MG
Selection: photon pt 750 1000 1250 1500 Each photon candidate is identified as a SC in ECAL. We require: SC pt > 100 GeV Born Box Brem QCD 750 1000 1250 1500 Higher pt photon Lower pt photon Born Box Brem QCD Red = All candidates Blue = MC Truth required
Selection: ECAL Isolation 750 1000 1250 1500 ECAL Iso = ET within cone of R < 0.5 ECAL Iso < 2% Plotted here are the Log of Ecal Iso Born Box Brem QCD 750 1000 1250 1500 Higher pt photon Lower pt photon Born Box Brem QCD Red = All candidates Blue = MC Truth required
Selection: H/E 750 1000 1250 1500 H/E = E of HCAL RecHits within cone of R < 0.3 / ET of SC H/E < 5% Plotted here are the Log of H/E Born Box Brem QCD 750 1000 1250 1500 Higher pt photon Lower pt photon Born Box Brem QCD Red = All candidates Blue = MC Truth required
Selection: Tracker Isolation, nTracks 750 1000 1250 1500 Tracker Isolation = number of tracks within cone of R < 0.3 nTracks <= 3 Plotted here are the Log of nTracks Born Box Brem QCD 750 1000 1250 1500 Higher pt photon Lower pt photon Born Box Brem QCD Red = All candidates Blue = MC Truth required
Selection: Tracker Isolation, pt Tracks 750 1000 1250 1500 Tracker Isolation = pT of tracks within cone of R < 0.3 / pT of SC pT of tracks / SC pT< 1% Plotted here is the Log of this variable. Born Box Brem QCD 750 1000 1250 1500 Higher pt photon Lower pt photon Born Box Brem QCD Red = All candidates Blue = MC Truth required
“Final” Selection Rates Selection rates after applying cascade of afore-mentioned cuts (%) With HLT1EMHighEt requirement Signal efficiencies ~40-50%, low (all <0.2%) background effiiency
“Final” Selection Rates Selection rates after applying cascade of afore-mentioned cuts (%) With HLT1EMVeryHighEt requirement Signal efficiencies ~40-50%, low (all <0.2%) background effiiency
Mass Distributions After Selection 750 1000 1250 1500 Born Box Brem QCD Numbers of events scaled to 1 fb-1
Next Steps Analysis: Production: Finalizing analysis and working on note based on MC studies Systematic Errors Comparison with ORCA results Currently, this is a simple MC analysis but we will eventually develop a more robust strategy for dealing with real data Production: 167: have produced signal with c=0.01, will include next 171: produced a couple samples before realizing huge memory usage in this release.. Noticed some large differences in efficiencies and selection variable distributions.. 172: just produced a few samples, currently checking Working on gamma+jets and 2gamma+jets Alpgen or CompHEP samples to better emulate backgrounds
Backup Slides
Comparison of HLT EG in 167 vs 171 E-gamma HLT path efficiencies Born Box 167 171 167 171 Appears that EG efficiencies in HLT have changed significantly from 167 to 171
167 vs 171 Selection: photon pt Born bkg Box bkg Higher Et photon Red = 167 Blue = 171 Lower Et photon
167 vs 171 Selection: ECAL Iso Born bkg Box bkg Higher Et photon Strange peaks Higher Et photon Red = 167 Blue = 171 Lower Et photon
167 vs 171 Selection: H/E Born bkg Box bkg Higher Et photon Red = 167 Blue = 171 Lower Et photon More narrow H/E distributions
167 vs 171 Selection: Tracker Isolation (pt_tracks) Born bkg Box bkg Significant change in tracker isolation distributions Higher Et photon Red = 167 Blue = 171 Lower Et photon
167 vs 171 Selection: Tracker Isolation (N_tracks) Born bkg Box bkg Decrease in tracking efficiency? Higher Et photon Red = 167 Blue = 171 Lower Et photon